netdev - [RFC PATCH 12/13] net: dsa: tag_gswip: let DSA core deal with TX reallocation

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Date:   Sun, 18 Oct 2020 00:36:10 +0300
From:   Vladimir Oltean <vladimir.oltean@....com>
To:     netdev@...r.kernel.org
Cc:     andrew@...n.ch, f.fainelli@...il.com, vivien.didelot@...il.com,
        kuba@...nel.org, Christian Eggers <ceggers@...i.de>,
        Kurt Kanzenbach <kurt@...utronix.de>,
        Hauke Mehrtens <hauke@...ke-m.de>
Subject: [RFC PATCH 12/13] net: dsa: tag_gswip: let DSA core deal with TX reallocation

Now that we have a central TX reallocation procedure that accounts for
the tagger's needed headroom in a generic way, we can remove the
skb_cow_head call.

This one is interesting, the DSA tag is 8 bytes on RX and 4 bytes on TX.
Because DSA is unaware of asymmetrical tag lengths, the overhead/needed
headroom is declared as 8 bytes and therefore 4 bytes larger than it
needs to be. If this becomes a problem, and the GSWIP driver can't be
converted to a uniform header length, we might need to make DSA aware of
separate RX/TX overhead values.

Cc: Hauke Mehrtens <hauke@...ke-m.de>
Signed-off-by: Vladimir Oltean <vladimir.oltean@....com>
---
 net/dsa/tag_gswip.c | 4 ----
 1 file changed, 4 deletions(-)

diff --git a/net/dsa/tag_gswip.c b/net/dsa/tag_gswip.c
index 408d4af390a0..cde93ccb21ac 100644
--- a/net/dsa/tag_gswip.c
+++ b/net/dsa/tag_gswip.c
@@ -63,10 +63,6 @@ static struct sk_buff *gswip_tag_xmit(struct sk_buff *skb,
 	int err;
 	u8 *gswip_tag;

-	err = skb_cow_head(skb, GSWIP_TX_HEADER_LEN);
-	if (err)
-		return NULL;
-
 	skb_push(skb, GSWIP_TX_HEADER_LEN);

 	gswip_tag = skb->data;
-- 
2.25.1